|Second, the purpose of the disposal field is to spread the liquid from the tank over a large underground area of soil, so the liquid can be absorbed or soaked up by the soil.|
Third, the purpose of the soil is to do the final treatment or purify the liquid from the tank.
Large numbers of tiny life forms called microbes live in the soil.
These microbes eat the remaining waste in the liquid.
This purifies the liquid so it is safe for humans and will not pollute drinking water or the environment.